The objective of this research is to study the electrical properties of the torso in man. The results of the study will be implemented in the development of a practical and accurate method to locate non-invasively an electrical dipole in the human torso. In certain arrhythmias, the region of an automatic focus behaves like an isolated dipole. It is anticipated that the developed method will be able to locate the origin of ectopic beats or other small areas of isolated myocardial activation. The properties of the volume conductor and the method for locating dipoles will be studied by using patients with implanted pacemakers. The implanted pacemaker simulates an isolated cardiac dipole and it can be located accurately by x-rays, thus it is very useful in studying the properties of the volume conductor in vivo, and in developing and testing in vivo the method for locating isolated cardiac dipoles. Secondary objectives of the research are to use the data collected from the patients with the pacemakers to test the accuracy of certain inverse algorithms, and to help in the preliminary tests of a new and general inverse algorithms that potentially can help in diagnosing most heart diseases like conduction blocks, hypertrophies and infarcts.